Using time-lapse VSP data to constrain velocity-saturation relations

Hosni, Mohammed Al; Caspari, Eva; Pevzner, Roman; Daley, Thomas M.; Gurevich, Boris

doi:10.1071/aseg2015ab153

Cited by 2 publications

(3 citation statements)

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“…; Al Hosni et al . ). These data are of high spatial resolution and provide constraints to the fluid distribution.…”

Section: Discussionmentioning

confidence: 97%

“…Hence, it is still under debate if it can be used as the representative fluid distribution at the reservoir scale. The sub-seismic-resolution saturation scale, if not captured by traditional flow simulators, should be determined from timelapse well log or VSP data (Sengupta, Mavko, and Mukerji 2003;Caspari et al 2011;Al Hosni et al 2015). These data are of high spatial resolution and provide constraints to the fluid distribution.…”

Section: Discussionmentioning

confidence: 99%

“…At the field scale, the fluid distribution can be indirectly identified from a velocity-saturation relation (VSR). The establishment of a field-scale VSR can be based on the well log/vertical seismic profile (VSP) data (Caspari, Müller, and Gurevich 2011;Al Hosni et al 2015) or the saturation profile from flow simulations . If the VSR follows prediction from Gassmann's equation (Johnson 2001), the fluid distribution is identified as uniform and otherwise patchy.…”

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confidence: 99%

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Saturation scale effect on time‐lapse seismic signatures

Müller

Gurevich

2016

Geophysical Prospecting

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Quantitative interpretation of time‐lapse seismic signatures aims at assisting reservoir engineering and management operations. Time‐lapse signatures are thought to be primarily induced by saturation and pressure changes. Core‐flooding and reservoir flow simulations indicate that a change of the driving forces during dynamic fluid injection gives rise to a varying saturation scale. This saturation scale is yet another variable controlling the time‐lapse seismic signal. In this work, we investigate the saturation scale effect on time‐lapse seismic signatures by analysing simple modelling scenarios. We consider three characteristic saturation scales, ranging from few millimetres to metres, which may form during gas injection in an unconsolidated water‐saturated reservoir. Using the random patchy saturation model, we compare the corresponding acoustic signatures, i.e., attenuation, reflectivity, and seismic gather associated with each saturation scale. The results show that the millimetre saturation scale produces minimum attenuation and the same seismic signatures with those obtained from the elastic modelling. The centimetre saturation scale produces maximum attenuation, whereas the metre saturation scale causes highest velocity dispersion. The analyses of the time shift and amplitude change indicate that ignoring a time‐dependent saturation scale can result in biased estimation/discrimination of the saturation and the fluid pressure. In particular, the 4D signal can be strongly affected by the saturation‐scale change when the reservoir gas saturation is low and the effective pressure is high. In the presence of an increasing (decreasing) saturation scale during injection, interpreting an observed time shift and amplitude change using the Gassmann model will lead to underestimation (overestimation) of the change in gas saturation and fluid pressure. We show that including the effects of capillarity and residual saturation into the rock physics modelling can potentially reduce the interpretation uncertainty due to the saturation‐scale change.

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“…; Al Hosni et al . ). These data are of high spatial resolution and provide constraints to the fluid distribution.…”

Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Saturation scale effect on time‐lapse seismic signatures

Müller

Gurevich

2016

Geophysical Prospecting

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Estimation of rock frame weakening using time-lapse crosswell: The Frio brine pilot project

et al. 2016

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[Formula: see text] injection into subsurface reservoirs leads to pressure and saturation changes. Furthermore, [Formula: see text]-brine-minerals interaction could result in dissolution or reprecipitation of rock frame-forming minerals. Observed time-lapse seismic associated with [Formula: see text] injection into poorly consolidated sandstone at the Frio [Formula: see text] injection site (Texas, USA) could not be predicted using classical rock-physics models (i.e., models involving elastic changes in the rock frame due to saturations and/or pressures changes only, and assuming no changes in the rock microstructure). That, and the changes in the fluid chemistry after [Formula: see text] injection, suggests that the assumption of a constant rock microstructure might be violated. Using high-resolution time-lapse crosswell data, we have developed a methodology for estimating changes in the rock frame by quantifying the rock-frame drained moduli before and after [Formula: see text] injection. Based on rock microstructure diagnostics, we found that the changes in the drained frame elastic properties are due to the changes in the grain contact-cement percentage. The reduction in contact-cement percent is found to be variable throughout the reservoir, with a maximum near the injection well, down to 0.01% from the initial 0.1% contact cement; this results in more than 40% reduction in the drained frame shear and bulk moduli. [Formula: see text] saturation was estimated using this model for uniform and patchy saturation cases. Our rock-physics analysis may allow improved interpretation of time-lapse seismic for [Formula: see text] saturation in the context of other poorly consolidated sandstones with similar geomechanical properties. Having the P- and S-wave velocity time-lapse data is key to improve saturation estimates with this analysis method.

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Using time-lapse VSP data to constrain velocity-saturation relations

Cited by 2 publications

References 11 publications

Saturation scale effect on time‐lapse seismic signatures

Saturation scale effect on time‐lapse seismic signatures

Estimation of rock frame weakening using time-lapse crosswell: The Frio brine pilot project

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